Patients with dementia often suffer from distortions of memory which impair their ability to live independently. This proposal will (1) investigate memory distortion in dementia patients by examining a) the susceptibility of patients with Alzheimer's disease (AD) and frontal lobe dementia (FLD) to illusory memories, and b) the neuroanatomical correlates of this susceptibility to illusory memories. Additionally, as treatments for specific dementias emerge, the need for simple, non- invasive diagnostic tests becomes imperative. Thus, this proposal will also (2) determine the clinical utility of an illusory memory test to distinguish FLD from AD. Experiments 1-3 test the hypothesis that patients with FLD are more susceptible than controls to illusory memories in semantic, perceptual, and pictorial false recognition paradigms. Experiments 4-6 test the hypothesis that patients with AD are less susceptible than controls to illusory memories using these same false recognition paradigms. Experiment uses single photon emission tomography to test the hypothesis that susceptibility to illusory memories correlates positively with perfusion defects in prefrontal regions and negatively with defects in medial temporal lobe regions. Experiment 8 tests the hypothesis that, because of the double dissociation predicted from Experiments 1-6, false recognition tests will distinguish AD and FLD patients equally or better than other methods. Collectively, these studies will provide both a better understanding of illusory memories in dementia as well as a potential new method of diagnosing patients with AD and FLD.